Serotonin (5HT) receptors are involved in critical aspects of human health and disease such as depression and migraine. Our long-term goals are to study the molecular pharmacology of these receptors, especially interactions between serotonin receptors and a significant cellular signal transducing scheme, the G protein system. In the present project, we propose studies with a type of human serotonin receptor known as the 5HTla receptor. This receptor belongs to a large superfamily of receptors which include other important model receptors such as adrenergic, dopaminergic, and muscarinic receptors. Based upon known properties of these model receptors and serotonin receptors themselves, we have synthesized and characterized a peptide from a putative G protein coupling region of the 5HTla receptor. In the present study we will utilize solid phase methods for synthesizing structural variants of this biologically active peptide. Activity of variants will be measured using agonist inhibition assays. Further functional assays will include determinations in changes of the second messenger cyclic AMP or the enzyme adenylyl cyclase, and by measurement of guanosine triphosphate (GTP)/ G protein binding. GTP binding assays will be performed in crude cellular preparations as well as in a cloned G protein system. Circular dichroism (CD) studies will analyze solution structures of priority peptides. Information from binding and functional experiments will contribute to determination of the best peptide tools for key molecular pharmacology studies of the interface. Advancements is analyzing and modeling molecular interfaces create a realistic opportunity for discovery of active conformations of receptor/G protein contact surfaces. Thus selected peptides will be used as probes of G protein using multi-dimensional nuclear magnetic resonance (NMR) to better understand the active conformations of the receptor-G protein interface. Information from our studies will add essential knowledge to modeling the receptor superfamily. Development of novel therapeutic drugs may follow.